Beetles, piñons shed light on ecology
In spring 2004, the Southwest landscape was littered with barren piñon pines after a drought ravaged the region. Anyone walking or driving through the high desert saw legions of toppled, rotting trees, with up to 80 percent of piñons wiped out in some areas. The final death blow for many of the pines was not the drought directly, but instead the piñon ips beetles that flourished over an unusually warm winter and subsequently feasted beneath the bark of drought-weakened trees.
As bad as things were, they could have been worse, were it not for population dynamics that likely put a damper on the ips bark beetle invasion initiated by the drought. The beetles are tiny, between 3 and 5 millimeters long at maturity, and a seemingly insignificant factor in understanding the environment. The fact that a full grasp of the planet’s ecology must take into account the behavior of such a minute insect is a testament to the complexity that’s involved in understanding the Earth’s environment.
In nondrought years, piñons
protect themselves by secreting resin sap that traps and kills attacking insects. When water is scarce, trees don’t have enough moisture to produce the sap to fight off parasitic beetles. That’s particularly true after a mild winter has allowed large numbers of beetle larvae to survive until the spring. The warmer temperatures and more intense droughts that accompany climate change substantially increase the risk of insect outbreaks, such as the piñon ips event in the Southwest and a more recent mountain pine beetle infestation that affected regions of North America from New Mexico to British Columbia, Canada.
Cold winters are one of the primary factors that keep mountain pine beetles in check. In warmer winters, more beetles survive, allowing them to expand beyond their native ranges. There are great concerns about the potential expansion of mountain pine beetle to the north and east of North America. However, the system is complex. Here’s the twist: The survival rate can be high enough in warm years that the beetles attack trees in numbers so large that they exceed the available resources. Juvenile beetles by the thousands swarming a single tree wind up starving before they can mature and move on to infest other trees.
In a study of pine trees in Alberta, Canada, Los Alamos ecologists found that despite the devastation the beetles often cause after an unusually warm winter, overcrowding slams the brakes on population growth, leaving some of the susceptible trees unscathed. The powerful overcrowding effect can make the damage from a beetle population explosion difficult to measure.
Climate-driven insect damage to forests can, in turn, exacerbate climate change. For example, the insects will cause the release of forest carbon back into the atmosphere, reduce the forest’s capability to capture carbon and change the environment’s energy balances. The loss of transpiration cooling by the trees can cause local warming in the insect-infested areas.
Adding bugs to Earth-system models
To get a fuller understanding of environments like the American Southwest, Los Alamos National Laboratory researchers are now including beetle population dynamics in Earth-system models alongside water cycles, temperature fluctuations, vegetation dynamics and other global and local factors. The best-known model is the Community Earth System Model, begun in 1960, which became the basis for the state-of-the-art Energy Exascale Earth System Model. E3SM is the Department of Energy’s opensource software that scientists use to simulate Earth’s past, present and future states.
E3SM involves more than a hundred researchers at eight national laboratories supported by the Department of Energy. It has more than 1.5 million lines of computer code that model chemical, physical, geological and biological processes within the Earth system, including the water cycle, energy and interactions among system components such as the atmosphere, oceans, ice and land cover. E3SM can be used to explore major trends and changes in the complex Earth system, which affect weather and climate-related extremes such as hurricane-induced flooding and long droughts.
In recognition of the importance of forests that globally absorb 30 percent of fossil fuel carbon released into the atmosphere, the Department of Energy national labs (Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, Pacific Northwest National Laboratory, Oak Ridge National Laboratory and Brookhaven National Laboratory) with funding from the Department of Energy Office of Science, joined efforts with the National Center for Atmospheric Research to create a demographic vegetation model. Named the Functionally Assembled Terrestrial Simulator (FATES), the model, which was added to E3SM in 2017, includes individual tree growth, death and competition for light; representation of both natural and man-made disturbances; and the dynamics among plant types as a result of their differing traits. The advanced representation of forests provides a more realistic simulation of tree defense against insect attacks in Earth system models.
Given Los Alamos National Laboratory’s mission to solve national security challenges through science, it has taken a lead in research and modeling drought. Drought reduces an ecosystem’s ability to absorb carbon and thus damages food sources. Drought also makes fires more likely and may spur major animal and human population movements. Among many other factors, Laboratory researchers are working to understand the flow of moisture in tree canopies and the carbon starvation that occurs when drought-stricken trees lack the water they need to perform photosynthesis. In that situation, trees wind up depleting their stored carbon reservoirs and are less able to defend against insect outbreaks.
The laboratory is actively working to contribute to and improve E3SM’s vegetation model.
Los Alamos’ vegetation research includes tropical forests, tundra shrubs in the Arctic, California fire and coastal wetland systems with salt marshes. No doubt those regions will have their own climate extremes and bugs, which will need to be studied for a better understanding of the future fates of our ecosystem and climates.